Detectors for detecting the presence of laser radiation are commercially available and have been widely discussed in the literature. A problem arises, however, when the radiation to be detected originates in a high power, Q-switched laser, for example, a neodymium laser operating at a wavelength of 1.06 .mu.m.
More specifically, detectors for detecting Q-switched laser radiation invariably include some sort of pulse-width discriminator circuit in order that any light pulse having a duration which is greater than 300 nanoseconds, say, will be rejected, since such a pulse cannot possibly originate in a Q-switched laser. However, if by chance the detector happens to be positioned in the path of the main laser beam, the detector will saturate, producing an output pulse having a duration which is too long for the pulse-width discriminator to process; thus, the pulse will not be detected, resulting in error.
Various complex and elaborate schemes have been used in the prior art in an attempt to overcome this problem. For example, circuits have been built which attempt to discriminate against the rise time of the input pulse, or which compare the ratio of pulse rise and fall time to pulse width. However, in either case, an engineering trade-off is made which sacrifices either sensitivity, dynamic range, or the false alarm rate.